The first sixth of the book relates the discussions between the protagonists justifying and plotting the revolution; the next quarter describes the year-long revolution itself. The remainder of the book recounts events occurring in the months after the revolution in May 2076, and a week or so of events in October 2076 leading up to capitulation by Earth.
Professor Bernardo de La Paz describes himself as a "Rational Anarchist", a name probably invented in the text itself. "Rational Anarchists" believe that the concepts of State, Society and Government have no existence but for the "acts of self-responsible individuals", but concede that this is not a universal belief. The desire for anarchy is balanced by the logic that some form of government is needed, despite its flaws. Knowing this fact, a Rational Anarchist "tries to live perfectly in an imperfect world". When challenged by Wyoh, Professor de la Paz replies, "In terms of morals there is no such thing as a‘state.’ Just men. Individuals. Each responsible for his own acts. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free, because I know that I alone am morally responsible for everything that I do."
Lunar society is portrayed as akin to that of the Old West, tempered by the closeness of death by exposure to vacuum and by the shortage of women. Because the sex ratio is about 2 men to each woman, the result is a society where women have a great deal of power, and any man who offends or touches a woman uninvited is likely to be attacked and eliminated through the nearest airlock. Marriages tend to be polyandrous, including group marriages and Mannie's own line marriage. In discussion with a woman from Kentucky, Mannie implies that underground, three-dimensional Lunar estate is recorded in the name of the woman (or women) in a marriage. In a divorce, he implies, the separated man (or men) who contributed towards its cost would have money returned to him.
After decades during which anti-social individuals were selectively eliminated and the Authority exercised little real control, the Loonies live by the following Code: Pay your debts, collect what is owed to you, maintain your reputation and that of your family. As a result, there is little theft, and disputes are settled privately or by informal Judges of good reputation. Failure to pay debts results in public shaming. Reputation is highly important in this society; with a bad reputation, a person may find others unwilling to buy from or sell to him. People are expected to pay back debts using all available funds.
Duels are permitted, but custom requires that anyone who kills another must pay debts and look after the deceased's family. Exceptions are allowed in the case of self-defense. Retaliatory killings do occur, but typically a consensus establishes which party was in the right, and there are no long-standing feuds. There is influence of the Vikings' mores on the Loonies, save that it is the society as a whole rather than the Althing which judges the actions of individuals.
Except where exchange involves the Authority, there is a generally unregulated free market. The preferred currency is the dollar of the Bank of Hong Kong Luna, one hundred of which are exchangeable for a troy ounce of gold, a supply of which was shipped to Luna for this purpose, or more usefully for potable water or other commodities in published quantities. The Authority dollar circulates in dealings with the Authority, but this tends to lose ground over time against the Hong Kong Luna dollar.
Although the revolution succeeds in averting ecological disaster, the narrator decries the instincts of many of his fellow Loonies ("Rules, laws– always for [the] other fellow"). This theme is echoed elsewhere in Heinlein's works– that real liberty is to be found among the pioneer societies out along the advancing frontier, but the regimentation and legalism that follow bring restraints that chafe true individualists (an idea emphasized in the first and final page of the novel, and in the later book The Cat Who Walks Through Walls ).
As in Stranger in a Strange Land , a band of social revolutionaries forms a secretive and hierarchical organization. In this respect, the revolution is more reminiscent of the Bolshevik October revolution than of the American, and this similarity is reinforced by the Russian flavor of the dialect, and the Russian place names such as "Novy Leningrad".
Continuing Heinlein's speculation about unorthodox social and family structures, The Moon Is a Harsh Mistress introduces the idea of a "line marriage". Mannie is part of a century-old line marriage, wherein new spouses are introduced by mutual consent at regular intervals so that the marriage never comes to an end. Divorce is rare, since divorcing a husband requires a unanimous decision on the part of all of his wives. Senior wives teach junior wives how to operate the family, granting financial security and ensuring that the children will never be orphaned. Children usually marry outside the line marriage, though this is not an ironclad rule. Mannie's youngest wife sports the last name 'Davis-Davis', showing she was both born and married into the line.
The social structure of the Lunar society features complete racial integration, which becomes a vehicle for social commentary when Mannie, visiting the southeastern United States, is arrested for polygamy after he innocently shows a picture of his multiracial family to reporters, and learns that the "range of color in Davis family was what got [the] judge angry enough" to have him arrested. It is later revealed that this arrest was anticipated and provoked by his fellow conspirators to gain emotional support from Loonies when the arrest is announced.
The novel is notable stylistically for its use of an invented Lunar dialect consisting predominantly of standard English and Australian colloquial words but strongly influenced by Russian grammar, especially omission of the article "the", which does not exist in most Slavic languages (cf. Nadsat slang from A Clockwork Orange by Anthony Burgess). This aspect of the Lunar dialect is explained by the fact that many of the deportees on Luna are Russian.
The novel indicates that Earth had experienced a nuclear world war (the "Wet Firecracker War") in the past century, although no significant traces of devastation are apparent at the time of the novel's setting.
Other changes include unification of the entire North American continent under a successor government to the United States, and political unification of South America, Europe, and Africa into mega-states. The Soviet Union seems to have lost the land east of the Urals to China into a rump state, and China has conquered all of East Asia, Southeast Asia, eastern Australia, and New Zealand (deporting unwanted people to Luna in the process). This Chinese aggrandizement is similar to that described in Tunnel in the Sky and, to a lesser extent, Sixth Column . The militarily dominant nations seem to be North America and China. India is overcrowded but seems able to obtain much of the wheat shipments from Luna.
It is suggested that the Western nations, including North America, have become corrupt and authoritarian, while holding on to the vestiges of the pre-war democratic idealism in propaganda and popular culture. China is portrayed as plainly and unabashedly despotic, but no less technically advanced than the West. The Soviet Union seems to have relatively little influence, whereas the Lunar Authority itself is portrayed as corrupt. Most of Earth seems to have been split into several large nations, most joined together by the Federated Nations. They include the North American Directorate, Great China, Soviet Union, Pan Africa, Brazil (hinted to include all of South America), and a European coalition (named "Mitteleuropa" in Chapter 25, Paragraph #8). Individual nations such as Chad (the first to recognize Luna), India, and Egypt are also named.